Catalytic waste gas converter for combustion machines

ABSTRACT

There is disclosed a catalytic waste gas converter for internal combustion engines of various types in which there is used as carrier for the catalyst a carrier matrix made of a steel screen arranged in a housing holder. There are employed special flow guides made of spirally wound steel matrices for the various flow through possibilities favorable to conversion of the waste gas to be purified.

This is a division of application Ser. No. 203,673 filed Nov. 3, 1980.

BACKGROUND OF THE INVENTION

The invention is directed to a catalytic waste gas converter forinternal combustion engines in which there is used as carrier for thecatalyst a carrier matrix made of steel screening and which throughspecial flow guides for the engine waste gas to be purified, the steelscreen matrix exhausts flow through possibilities inherent in thosematrices.

The toxic materials of waste gases especially waste gases from internalcombustion motors of the steadily increasing number of motor vehiclesrepresents a considerable danger to the health of men, animals andplants. They are limited in several countries by the legal regulation tomaximum concentrations of toxic material. Among the solutions proposedfor these air pollution problems and already practiced methods, thecatalytic waste gas purification process has acquired the greatestimportance. Greatest demands have been placed on the catalysts requiredtherefore in regard to behavior on heating, effectiveness, lastingactivity and mechanical stability. For example, when employed in motorvehicles, they must be effective even at the lowest possibletemperatures and guarantee a high percentage reaction of the toxicmaterials to be removed (especially hydrocarbons, carbon monoxide andnitric oxide as well as aldehydes, alcohols and carbon black) to formthe non-toxic oxidation and reduction products carbon dioxide, steam andnitrogen for a long time at all temperatures and space velocities whichare used. Because of the severe mechanical requirements during theoperation, they must possess a sufficient mechanical stability and arepermitted not be be lost even with long overheating, as can occur in agiven case through being acted on by unburned fuel, for example, inignition loss in one or more cylinders. Thus, they must satisfy a numberof conditions which are difficult to fulfill simultaneously or runcontrary to one another.

Previously, besides poured bed catalysts, i.e., or extrudates ofcatalyst carriers or interspersant or mixed catalysts there were usedabove all, monolithic catalyst carriers. They consist of an inert, lowsurface area ceramic skeleton of, e.g. cordierite, mullite or α-aluminumoxide as structural reinforcer to which there is applied a thin, usuallyhigh surface area layer of a heat resistance, usually oxidic carriermaterial such as aluminum oxide of the so-called gamma series, whichlatter in turn carries the true catalytically active components. Thesecan consist of noble metals, noble metal compounds or non-noble metalcompounds. Of the group of noble metals, there are employed for exampleplatinum, palladium, rhodium, ruthenium, iridium, gold and silver.

As non-noble metal compounds there are employed, e.g. the oxides ofcopper, chromium, manganese, iron, cobalt, nickel and their combinationsas e.g. copper chromite. Further variants are formed by combining noblemetals or their compounds with non-noble metals or their compounds ornon-noble metals or their compounds with noble metals or theircompounds. In many cases there are added to the active components smallamounts of other elements, for example, from the group of alkaline earthmetals such as magnesium, calcium, strontium or barium, from the groupof rare earths, as e.g. samarium, lanthanum, cerium or from the fourthgroup of the periodic system, as, e.g. titanium, zirconium or tin, asso-called promoters for improving specific properties of the system.

As a considerable disadvantage of the catalyst having ceramic structuralreinforcers, especially the monolithic honeycomb catalysts ofcordierite, mullite or α-aluminum oxide, there has proven their poorheat conductivity and their sensitivity to mechanical influences andthermal overheating. Thus the vibrations occurring during travelingthrough the intermittent impulse of the waste gas columns, the motorvibration and the traveling motions in combination with temperaturepeaks act to wear down and crumble the ceramic. With thermal overheatingin the spatially narrowly limited monoliths there can occur sintering,melting and fusing of the structural reinforcer in the form of monolithsor poured bodies with its coatings from which partial or completeinactivation results.

Furthermore, it has been proven that installing such ceramic honeycombsin metal housings is difficult because of the different thermalexpansion of ceramic and metal and requires expensive constructionprecautions in order to guarantee an elastic and gas tight holding ofthe honeycomb with the relative motions at the continuously changingoperating temperatures in the possible range between -30° and +1000° C.

Therefore, there has been a series of efforts to find better suitedreplacement materials for the catalyst built on a ceramic basis and tolook for a more favorable spatial designing for these.

Thus there has already been described a carrier matrix which is preparedfrom an alternatively arranged corrugated and smooth high temperatureresistant steel sheet which is coated with catalyst. However, in thiscase, there is the disadvantage that the carrier has a limitedgeometrical surface which limits to such an extent the supportingcapability compared to catalyst carrying, high surface area, heatresistant metal oxides, such as γ-Al₂ O₃, present in immersed dispersionthat to produce a sufficiently strong coating on these oxides with theactually catalytically active components there is needed a many timesrepeated immersion process. Since the known carrier matrices are passedthrough by flow channels separated from one another, the reacting gasmixture only comes in contact with the catalyst material in the form ofindividual enclosed, longitudinally flowing gas columns from the walls;through this with predetermined gas flow velocity there is required aspecific, frequently too large minimum length of the matrix in order toproduce a satisfactory exchange of material and connected therewith asufficient degree of conversion.

Subsequently, there occurs between the individual longitudinally runningdiscrete reaction zones a drop in temperature for example because oflocal more or less different layer thicknesses and activities of thecatalyst material which can only be equalized via the specific heatconductivity of the material of the channel wall.

According to German patent application P 2853547.9, and correspondingU.S. Ser. No. 102,581, filed Dec. 11, 1979, now U.S. Pat. No. 4,271,044,the problem of providing carrier matrices for catalysts having flowchannels passing therethrough consisting of superimposed layers of hightemperature resistant and scale resistant steel, which permits a crosscurrent between the individual flow channels, has an enlargedgeometrical surface and shows an improved supporting capability comparedto catalyst carrying carrier materials present in immersing dispersions,is solved by constructing the matrix of alternating layers of smooth andcorrugated screens (sieve netting) whereby the layers are coiled to acylinder having a spiral cross section and having numerous flowchannels.

In consideration of the fact that in such coils in addition to thenormally longitudinally flowing channels of the motor waste gas to bepurified, there also is permitted via the openings of the screens across current to adjacent channels (so-called cross current effect)there is a need of holding apparatuses for such matrices which permitthe utilization of these inherent flow possibilities in a more favorablemanner.

SUMMARY OF THE INVENTION

According to the invention there is designed a catalytic waste gasconverter for internal combustion engines of various types in whichthere is used as carrier for the catalyst, a carrier matrix made of asteel screen (or sieve netting) arranged in a housing holder andemploying special flow guides made of spirally wound steel matrices forthe various flow through possibilities favorable to the conversion ofthe waste gase to be purified. The objects of the invention are realizedfor example by various types of catalytic converters shown in thedrawings. In the various developments of the invention the statedindividual types of fastening for the represented screen matrix havingalternating smooth and corrugated screen layers which is an essentialcomponent of the converter should be interchangeable with each other.

In regard to the winding or coiling of the carrier defined in the claimsthe type of manufacture, selection of material, pretreatment as well ascoating with catalyst carrying metal oxides and catalyst compositions,there can be used for example, those disclosed in the two German patentapplications P No. 2853547.9, mentioned before and P No. 2908671.3. Theentire disclosure of these two German applications is herebyincorporated by reference and relied upon.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a schematic longitudinal sectional view of a converterembodying this invention in which there is an impingement of thecylindrical or tubular catalyst-carrying matrix with waste gas both onits upstream end, via the upstream openings in the gas inlet tubeoutside the matrix, and on the walls of the central opening extendingtherethrough, via the perforated section of the gas inlet tube extendinginto the matrix, and a flowing off or exit of the gas from both theentire outer periphery of the matrix and its downstream end.

FIG. 2 is a view similar to FIG. 1 of a modification of the invention inwhich the perforated section of the gas inlet tube is replaced with aseparate perforated cylinder.

FIG. 3 is a cross-sectional view of the converter shown in FIG. 1.

FIG. 4 is a cross-sectional view of the converter shown in FIG. 2.

FIG. 5 is a view similar to FIG. 1 of another modification of theinvention wherein the impingement of the tubular matrix with waste gastakes place as shown in FIGS. 1 and 2 but the flowing off or exit of thegas takes place only from the downstream end of the tubular matrix.

FIG. 6 is a view similar to FIG. 5 of another modification of theinvention in which the perforated section of the gas inlet tube isreplaced with a separate perforated cylinder.

FIG. 7 is a view similar to FIG. 1 of another modification of theinvention in which the impingement of the tubular matrix with waste gasoccurs only on the walls of the central opening through the matrix, viathe perforated section of the gas inlet tube, and the flowing off orexit of the gas takes place from both the downstream end of the matrixand its entire outer periphery.

FIG. 8 is a view similar to FIG. 1 of another modification of theinvention similar to that of FIG. 7 but wherein the perforated sectionof the gas inlet tube is replaced by a separate perforated cylinder.

FIG. 9 is a view similar to FIG. 1 of another modification of theinvention in which impingement of the tubular matrix with waste gastakes place only on the walls of the central opening extending throughthe matrix, via the perforated section of the gas inlet tube, and thegas exits from the matrix only from its entire outer periphery.

FIG. 10 is a view similar to FIG. 1 of another modification of theinvention similar to FIG. 9 but wherein the perforated section of thegas inlet tube is replaced by a separate perforated cylinder.

FIG. 11 is a view similar to FIG. 1 of still another modification of theinvention in which impingement of the tubular matrix with waste gasoccurs only about its entire outer periphery, via a perforated matrixjacket, and the gas flows off or exits only from the inner wall of thematrix, i.e., only through the central opening therethrough, via aperforated gas removal tube.

FIG. 12 is a view similar to FIG. 1 of another modification of theinvention similar to that of FIG. 11 but wherein the perforated sectionof the gas removal tube is replaced by a separate perforated cylinder.

DETAILED DESCRIPTION

According to FIGS. 1-4, the container of the waste gas converterincludes a cylindrical housing section 1 having at its upstream end afrusto-conical cover 2 and at its downstream end a frusto-conical cover30. A holding plate 3 having inner and outer flat rings connected byradial spokes 10 is fastened within the container at the transition orintersection 9 between the cylindrical housing section 1 and the cover2. Extending through the cover 2 and the inner ring of the holding plate3 is a cylindrical gas inlet or supply tube 4 closed at its inner end,as at 4'. At its upstream end, the tube extends out of the cover 2. Theclosed downstream end 4' of the tube 4 is substantially at the plane ofthe transition or intersection between the cover 30 and the housingsection 1. That section of the tube 4 extending within the cover 2 isprovided with a plurality of longitudinally elongated openings 14. Thesection of the tube 4 extending downstream beyond the holding plate 3 isprovided with a plurality of perforations 14' and carries thecatalyst-carrying tubular matrix 5 in the form of a coil of alternatingsmooth and corrugated steel screens, with the corrugations extendinglongitudinally of the coil. This perforated section of the gas inlettube 4 can be replaced by a separate perforated cylinder 16 closed atits downstream end, as shown in FIG. 2. In such construction, the gassupply tube 4 extends into and terminates just below the upstream end ofthe cylinder 16, as at 17, and is welded to the holding plate 3, as at9.

The steel screen of the coil 5 preferably is made of high temperatureresistant and scale resistant steel. The outer diameter of the coil 5 isless than that of the section 1 and only slightly larger than the innerdiameter of the outer ring of the holding plate 3. The tubular matrix orcoil 5 is supported at its downstream end by a plurality of radialflanges 6 which are secured to and within the cover 30. The matrix orcoil 5 has a large geometric surface area and a good catalyst supportingcapability as compared to catalyst supporting carrier materials presentin immersed dispersion. For example, the screens of the coil 5 arecoated with γ-Al₂ O₃ in which case the coating, usually in a layerapplied by the wash coat process, supports a catalytically activecomponent containing the elements platinum, rhodium and/or aluminum.There can be used, however, all of the catalyst supporting carriermaterials and catalyst compositions proposed for the purification of theexhaust gases of internal combustion engines, as are described in theaforementioned German patent applications P No. 2853547.9 and P No.2908671.3.

To strengthen the coil 5, it is enclosed in a perforated cylinder 7which is attached to the periphery of the coil. The cylinder is weldedto the outer ring of the holding plate 3, as at 18. A short gaswithdrawal or exit tube 8 is secured to the apex of the frusto-conicalcover 30, as at 19. The spokes 10 of the holding plate 3 preferably arearranged in the form of a cross, as shown in FIG. 3, while the outerring of the holding plate is wide enough to provide an adequate annularflow channel 11 between the cylinders 1 and 7 for the flowing off orexiting of the gas from the entire outer periphery of the matrix 5. Inthe embodiment shown in FIGS. 1 and 2, the gas also flows or exits fromthe downstream end of the coil 5. The several layers of the coil 5preferably are welded or soldered together at spaced intervals at itsupstream end 12 and also at its outer circumference 13. It should beemphasized, however, that such welding or soldering can be reduced oreliminated since the coil is supported sufficiently between the holdingplate 3 and the flanges 6 and between the tube 4 or cylinder 16 and theouter perforated cylinder 7. The inner layer of the coil, however,should be welded to the gas supply tube 4 or the cylinder 16.

The assembly of the waste gas converter shown in FIGS. 1 and 2 isaccomplished as follows:

The longitudinal edges of the innermost alternating smooth andcorrugated layers of the steel screen of the coil 5 are welded to theperforated section of the gas supply tube 4, or to the cylinder 16.Subsequently the screens are wound into the finished coil 5. Thefinished coil or carrier matrix 5 then is inserted into the perforatedcylinder 7. Then, according to requirements, the interleaved, smooth andcorrugated layers, or turns, can be welded together at various spacedintervals at the inlet end of the coil. Similarly, the outer layers orturns of the coil 5 can be welded to the outer perforated cylinder 7.The outer cylinder 7 of the finished carrier body is welded, as at 18,to the carrier plate 3. Likewise, the gas supply tube 4 is welded to thecarrier plate 3, as at 9. Along with these operations, the cylindricalcontainer or housing section 1 is welded to its frusto-conical cover 30and the latter welded to the gas withdrawal tube 8, as at 19. The crossshaped holding flanges 6 are welded in place within the conical cover30. Then the carrier matrix 5, with the gas supply tube 4 and holdingplate 3, are inserted into the housing section 1 and welded together asat 9. Subsequently, the conical cover 2 is welded to the housing plate 3and to the gas supply tube.

The embodiments shown in FIGS. 5-12 are alternative constructions to theembodiments shown in FIGS. 1 and 2. The embodiments of FIGS. 5-12 differfrom those shown in FIGS. 1 and 2 by different flow paths for the wastegas and different types of holders for the carrier matrix 5.

In the embodiments shown in FIGS. 5 and 6, the outer cylinder 7 isomitted and the outer periphery of the tubular matrix 5 is disposedclosely adjacent the cylindrical housing section 1 with a layer ofthermal insulation 20 therebetween. Further, the holding plate 3 isomitted and replaced with supporting flanges 106, like the flanges 6.This construction of the converter permits both longitudinal flow of gasthrough the matrix 5, and also flow laterally outwardly into the matrixfrom the central opening therethrough and thence longitudinallyoutwardly from the downstream end of the matrix. In other words, thereis both longitudinal and lateral flow of the gas into the matrix 5 butthe gas exits only longitudinally from the downstream end of the matrix.Preferably, the insulating material 20 is ceramic felt and the matrix 5is not welded to a holding plate but is supported at its upstream anddownstream ends, respectively, by the flanges 106 and 6.

In the embodiments shown in FIGS. 7 and 8, the annular holding plate 3ais imperforate and welded, as at 9, to both the inlet tube 4 and theedge of the frusto-conical cover 2. That section of the gas supply tube4 disposed within the cover 2 has no openings therein, i.e. isimperforate, and has perforations only in that section thereof extendingwithin the tubular matrix 5. The outer diameter of the carrier matrix 5is smaller than that of both the housing section 1 and the holding plate3a in order to form an annular gas exit channel 11 between the matrix 5and the housing section 1. At its closed end 4' the gas supply tube 4 issecured in notches 21 in the supporting flanges 6. This modificationadmits waste gas to the tubular matrix 5 only through the perforatedsection of the inlet tube 4, i.e., only from within the central openingthrough the coil 5. The purified waste gas exits from the coil 5 bothinto the annular channel 11 and at the downstream end of the matrix 5,so that there is both a lateral and longitudinal exit of the gas fromthe tubular matrix 5. The matrix 5 is supported, without welding,between the holding plate 3a and the flanges 6. The notches 21, in thelatter, prevent lateral displacement of the closed end of the gas supplytube which projects somewhat beyond the tubular matrix 5.

In the modifications shown in FIGS. 9 and 10, an annular imperforateholding plate 3a is secured, as at 9, to both the gas inlet tube 4 andthe larger end of the cover 2. Between the cylindrical housing section 1and the outlet cover 30 a holding plate 3b is welded to the gas supplytube 4 as at 109. The plate 3b has a circular array of openings 22 inits marginal outer edge portion through which gas exits from the annularchannel 11. The annular channel 11 is formed because the outer diameterof the tubular matrix 5, as in the converter shown in FIGS. 7 and 8, issmaller than the diameter of the holding plates 3a and 3b. In thisconstruction, there is only a lateral outward flow of the gas throughthe matrix from the central opening therein to the annular channel 11.Further, the tubular matrix 5 is supported endwise only by the holdingplates 3a and 3b and lateral displacement is prevented by slightlylengthening the gas supply tube 4.

In the embodiments shown in FIGS. 11 and 12, a first circular holdingplate 113b is provided with gas inlet openings 22 only in an annularouter marginal edge portion. The plate 113b is secured, as at 9, to thelarger end of the frusto-conical 2 and to the upstream edge of thecylindrical housing section 1. An annular imperforate holding plate 113asupports the downstream end of the cylindrical matrix 5 and is secured,as at 9, to both the downstream edge of the cylindrical housing section1 and the corresponding edge of the downstream cover 30. The plate 113asurrounds a gas exit tube 4, and is secured thereto, as by welding, asat 109. The tube 4 extends upstream through the central opening in thematrix to the holding plate 113b and abuts this in gas tight relation.At its downstream end, tube 4 extends out of the frusto-conical cover30. That section of the tube 4 disposed within the central opening inthe matrix 5 is perforated for admission of gas thereinto from thematrix 5. In this embodiment, there also is formed an annular channelbetween the periphery of the tubular matrix 5 and the cylindricalsection 1. The cover 2 has a short gas inlet tube 8 at its apex andpreferably a distribution cone 23 is disposed within the cover 2 so thatgas entering the latter will be better distributed to the openings 22for flow therethrough into the annular channel and thence radiallyinwardly through the perforations in the cylinder 7, through the tubularmatrix 5, and thence through the perforations in the gas exit tube 4.

In this modification, it will be seen that gas flows through the tubularmatrix 5 only from its outer periphery laterally inwardly therethroughinto its central opening. Preferably the perforated outer cylinder orcasing 7 of the matrix 5 is welded to the downstream holding plate 113a,as at 18, to prevent lateral displacement of the matrix.

The above described converter constructions are useful with narrow meshcoil screens coated with porous carriers of catalyst compositions ascatalytic filters for the purification of carbon containing dieselengine waste gases in which the carbon particles are filtered from thewaste gas stream and the volatile materials converted to innocuousproducts by catalytic action.

The entire disclosure of German priority application P No. 2922841.7 ishereby incorporated by reference.

The converter can comprise, consist essentially of or consist of thestated elements.

The smooth and corrugated or undulating steel screen can have a meshaperture of 0.5 to 2.5 mm, preferably 0.8 to 1.6 mm, especially 1.0 mmand a wire thickness of 0.2-0.4 mm (e.g., 0.26 mm), preferably 0.2-0.3mm, especially 0.25 mm.

What is claimed is:
 1. A catalytic waste gas converter suitable for theuse with an internal combustion engine or a diesel engine comprising incombination a cylindrical housing with gas inlet means at one endthereof and gas withdrawal means at the other end thereof, a firstconical cover at the gas inlet end of the housing and a second conicalcover at the gas withdrawal end of the housing, a gas supply tubepassing through the cover on the gas inlet end of the housing andextending up to the plane of a first transition between the cylindricalhousing and the cover at the gas withdrawal end of the housing, said gassupply tube being closed at the end thereof, the section of the gassupply tube before a second transition between the housing and the coverat the gas inlet of the housing having openings at the circumference andthe section of the gas supply tube lying below said second transitionhaving perforations, a coil surrounding the perforated section of thegas supply tube and being made of catalyst coated, alternating smoothand undulating layers of a high temperature and scale resistant steelscreen, said coil being supported on its downstream face by flange meansfastened to the cover on the gas withdrawal side and on its upstreamface by flange means fastened to the cover on the gas inlet side, aninsulation layer disposed on the periphery of said coil, said coil andinsulation layer being in the form of a roll in the cylindrical housingand a gas withdrawal tube attached to the cover on the gas withdrawalend of the housing.
 2. A waste gas converter according to claim 1wherein the layers of the catalyst coil are at least partially solderedor welded together at their front sides.
 3. A waste gas converteraccording to claim 2 wherein the first layer of the catalyst coil iswelded or soldered to the gas supply tube.
 4. A waste gas converteraccording to claim 1 wherein the first layer of the catalyst coil iswelded or soldered to the gas supply tube.
 5. A waste gas converteraccording to claim 1 wherein the respective flange means for thecatalyst coil are welded or soldered to the conical covers.
 6. A wastegas converter according to claim 1 wherein the gas supply tube is weldedor soldered to the first conical cover and the gas withdrawal tube iswelded or soldered to the second conical cover.
 7. A catalytic waste gasconverter suitable for use with an internal combustion engine comprisingin combination a cylindrical housing with gas inlet means at one endthereof and gas withdrawal means at the other end thereof, a firstconical cover at the gas inlet end of the housing and a second conicalcover at the gas withdrawal end of the housing, a gas supply tubepassing through the cover on the gas inlet end of the housing andterminating at the transition between the housing and the first conicalcover, said gas supply tube opening into one end of a perforatedcylinder which is closed at the other end thereof, the perforatedcylinder extending to the plane of transition between the cylindricalhousing and the cover at the gas withdrawal end of the housing, a coilsurrounding the perforated cylinder and being made of catalyst coated,alternating smooth and undulating layers of a high temperature and scaleresistant steel screen, said coil being supported on its downstream faceby flange means fastened to the cover on the gas withdrawal side and onits upstream face by flange means fastened to the cover on the gas inletside, an insulation layer disposed on the periphery of said coil, saidcoil and insulation layer being in the form of a roll in the cylindricalhousing and a gas withdrawal tube attached to the cover on the gaswithdrawal end of the housing.
 8. A waste gas converter according toclaim 7 wherein the layers of the catalyst coil are at least partiallysoldered or welded together at their front sides.
 9. A waste gasconverter according to claim 7 wherein the gas supply tube is welded orsoldered to the first conical cover and the gas withdrawal tube iswelded or soldered to the second conical cover.
 10. A waste gasconverter according to claims 1 or 7 wherein the steel screen has a meshaperture of 0.5 to 2.5 mm and a wire thickness of 0.2 to 0.4 mm.
 11. Awaste gas converter according to claim 10 wherein the steel screen has amesh aperture of 0.8 to 1.6 mm and a wire thickness of 0.2 to 0.3 mm.